The PET resin has excellent physical properties and the production amounts are stable. Thus, being supplied at relatively low cost, the PET resin is in widespread use as beverage and food containers such as PET bottles. Used PET bottles are separated and collected, and reused as a recycled polyethylene terephthalate resin (hereinafter, also referred to as a recycled PET resin). With an established recycle technology of PET bottles, the recycled PET resin can be used as the stable material.
Having the thermal history of being heated and melted during the process of recycle, the recycled PET resin has its molecular chains cleaved and its polymerization degree degraded. For this reason, the recycled PET resin is unusable for a molded item that requires reliability. In addition, the polymerization degree of the recycled PET resin degraded, and the melt viscosity is low, so that it is not suitable for extrusion molding. Because its crystallization rate is slow, the recycled PET resin generates spherocrystals at low temperatures to become brittle, when the extension in molding is not enough. In order to solve these problems, attempts to improve the physical properties of the recycled PET resin are made by mixing various different kinds of polymers with the recycled PET resin (see PTL1 to PTL5).